This invention relates to a brake control system, and more particularly to anti-jackknifing and skidding controls for a vehicle having a cab and a trailer portion.
One of the major problems faced by truck users is the possibility of jackknifing wherein the trailer portion of the truck skids sideways out of control of the driver. This problem is frequently caused by dangerous road conditions such as ice, water, snow, or mud, taken by themselves and/or possibly in combination with an improper maneuver made by the driver in an emergency situation. With the increased use of trailer trucks on superspeed highways, the possibility of damaging the truck as well as causing a severe traffic accident has made the skidding and jackknifing problem most serious.
This problem has caused federal and state governments to institute strict requirements which effectively call for straight line stops and a minimum of side to side motions. These requirements can be met generally with some form of electronic anti-skid system which basically prevents the possibility of jackknifing and skidding problem. The known brake systems are complex and frequently rely on computers as well as sensors to prevent brakes from locking. Also, these systems generally require the sensors to be mounted in a predetermined relationship to the wheels and also provide direct control to the brake system in the vehicle to apply braking action on all of the wheels equally. Also, most of these systems act to usurp control of the existing brake system away from the driver.
The jackknifing and skidding problem is not unique to trailer trucks since skidding can occur on a standard type automobile as well. However, in a standard two-axle vehicle, should skidding occur, it suffices to turn the front wheels into the direction of the skid to alleviate the skidding problem. The turning of the wheels into the direction of the skid provides a suitable opposing torque, to that created by the skid, which frequently remedies the skidding problem. However, this solution will not work in a multi-axle truck of the tractor-trailer type, and, in fact, a maneuver of the cab or tractor itself has but negligible effect upon the trailer portion should the skid occur in the trailer part of the vehicle.
U.S. Pat. No. 3,288,240 has suggested the use of a mercury switch in the trailer portion of a towed vehicle and, based upon the direction of lateral sway, for example, a differential type braking is applied to either the right or left wheels of the trailer. This approach of differential braking may be useful in alleviating swaying or swerving problems. However, the stability control system described in the aforementioned patent cannot differentiate between a coordinated turn and a jackknifing condition. For example, a truck driver traveling on a highway containing sharp curves will maneuver the truck around the curves at almost regular highway speeds. The accelerometer will detect lateral acceleration of the trailer and will interpret it as being a skidding or jackknifing condition. It will then apply a differential braking to the wheels on one side of the truck which will actually initiate a skidding condition and will force the truck to skid or jackknife into an adjacent lane, thereby causing accidents to occur.
Furthermore, in applying the automatic stability control of the aforementioned patent, when a jackknifing condition is sensed, differential braking will be continuously applied until the acceleration has ceased. However, for severe skidding and jackknifing conditions such continuous braking may cause the wheels to lock which would again make the condition worse rather than improving it.